As an exhaust gas purification filter provided in an exhaust system such as a diesel engine, a Diesel Particulate Filter (DPF) has been known that collects a Particulate Matter (PM) such as soot or the like contained in an exhaust gas.
When a PM collection capability of the DPF is deteriorated due to the breakage or the like, the PM, which is not collected by the DPF and is slipped through the DPF, is emitted in an atmospheric air, so that it is possible that an exhaust gas regulation value cannot be satisfied. For this reason, there is a demand to perform an on-board diagnosis of the failure of the DPF.
As a technique for determining the failure of the DPF, for example, there is known a method in which a resistive type PM sensor is provided at a downstream side of the DPF to compare a sensor value and a reference threshold (see, for example, PATENT LITERATURE DOCUMENT 1).